The present invention relates to a spindle control device, and particularly to a spindle control device in an optical disk recording/reproducing apparatus in which one frame of a composite video signal (including synchronizing signals such as a horizontal synchronizing signal, a vertical synchronizing signal, and the like) is recorded on each track on an optical disk (including an opto-magnetic disk and a phase-change type optical disk) having a vertical synchronizing mark, and in which the recorded signal on the optical disk is reproduced or erased.
In a conventional reproducing-only video disk player, since an optical disk to be played carries a composite video signal already recorded thereon, the composite video signal is read from the optical disk and demodulated. A phase difference of a reproducing horizontal synchronizing signal included in the demodulated composite video signal relative to a reference horizontal synchronizing signal is detected so as to perform spindle servo control in accordance with the detected phase difference.
On the other hand, in a system in which one frame of a composite video signal is recorded on each track on an optical disk and the recorded signal is reproduced or erased, no composite video signal exists on the disk before recording. As a result, spindle servo control cannot be performed by use of a reproducing horizontal synchronizing signal, unlike the above-mentioned reproducing player. Accordingly, a vertical synchronizing mark VM made of a mirror portion where no pregroove G is cut is provided, one for every rotation on a disk, for example, at its inner circumference (or at its outer circumference) as shown in FIG. 1. The vertical synchronizing mark VM is detected by a vertical synchronizing mark detector, such as a photocoupler or the like, during a recording operation, and spindle servo control thus is performed so as to make the detection timing of the vertical synchronizing mark VM agree with a predetermined position on the time base of the composite video signal to be recorded. As a result, the irradiated position with a recording light beam, modulated in accordance with the composite video signal, is controlled to be a predetermined position in the circumferential direction of the disk at the detection timing of the vertical synchronizing-mark detector.
In such a system, phase control of the spindle motor is performed so as to make the spindle motor synchronous with an external composite video signal during a recording/erasing operation, while phase control of the spindle motor is performed so as to make the spindle motor synchronous with an external composite video signal or an external synchronizing signal in the case of external synchronizing drive, even during a reproducing operation. At that time, in the case where an external synchronizing source signal is not supplied for some reason or other, phase control of the spindle motor becomes unstable because there is no synchronizing source. Accordingly, there is a possibility of spindle motor runaway operation.
Further, in starting the system, phase control of the spindle motor cannot be started .before the vertical synchronizing mark VM is detected normally. In the case where a disk having a different format is set erroneously, similarly to the above case, there is a possibility of spindle motor runaway operation.